Appendix B 1 Progress report of the network ”Mesoscopicsolid state and molecular electronics”, Description of activities

a) Summary of year 2003, results compared with plans

The main planned activity for year 2003 was a network meeting in Röst, Norway. Thatworkshop did take place as planned in conjunction with another Norfa network“Fundamental quantum processes in atomic and molecular systems”, coordinator Jan-Petter Hansen, Univ. of Bergen. The meeting was very successful and unique because itcombined activities of two separate networks. Our network’s attendance was slightlylower than expected, thus not all the budgeted money was used. Also, severalindividual collaborative visits took place, measured in money these visits also didn’tquite reach the budgeted level. Thus, some surplus was accumulated in 2003.

b) Mobility within the network, 2003

The network’s mobility activity is described below group by group:

Lindelöf group:

There has been a considerable travelling between Lund (Chao's group)and Copenhagen (Lindelof's group) (typically 1-day meetings. This isalso strongly encouraged by the so called Oeresund Initiative. Ameeting (in Brussels) about a new European STREP project "ULTRA-1D"involving the Jyväskylä groups and the Copenhagen group and others canbe considered a result of the intensive NORFA collaboration.

The Chalmers group had the following visits within the network:

J Kinaret A.P. Jauho, Copenhagen, 2 days C Huldt A.P. Jauho, Copenhagen, 2 days A. P. Jauho J. Kinaret, Gothenburg, 2 days R.I. Shekter Y. Galperin, Oslo, 5 days Y. Galperin R.I. Shekhter, Gothenburg, 4 days

Helsinki groups had following visits:

Hakonen, Chalmers, Delsing + Kinaret, Nov. 2 - 5, 2003Paalanen, Chalmers, Kinaret (+CARAMEL consortium members), Oct. 27,2003.Pekola: Several visits to Univ Jyväskylä, two visits to CTH. Savin(Pekola group) Visit to CTH Kiruna school organised by Leonid Kuzmin.

Jauho group:

Tomas Novotny and Andrea Donarini visited Chalmers inDecember/January.Tomas Novotny and Christian Flindt attended the network meeting.

Chao group (Lund):

Vladislav Schlyapin attended the 2003 Annual Meeting and gave an oral presentation of our work. Prof. A. G. Mal'shukov visited Lund forthree months (Oct-Dec 2003) with finances from other sources. Dr. C. H. Chang visited Lund for three months (Oct-Dec 2003) withpartial financial support from the Network Budget.

Galperin, Oslo

Daniel Shantsev (Ioffe Physico-Technical Institute, St.Petersbrug,Russia) works at the University of Oslo under supervision of Yuri M.GalperinPeriod: 01.10.2002-30.09.2003 Thomas Kühn (Department of Physics, University of Jyväskylä) visits Y.M. Galperin and D. V. Anghel, at the University of Oslo.Period: 5.05.2003 – 30.05.2003.

Brataas, Trondheim:

Participants from my surroudings to Roest where Jan Petter Morten andJan Manschot from Trondheim and Gerrit E. W. Bauer and Alexey Kovalevfrom Delft.

Gudmundsson:

Jens H. Bardarson did participate in the Rost meetingfor the group.

Maasilta (new member)

Maasilta visited Chalmers 24.2 (1 day) and attended the Röst meetingEnd of August. In addition as described above, Thomas Kuhn (PhDstudent) spent a month in May with the Oslo group.

c)Supervision of research students and e) List of members of the network

Each member group is listed with its present supervised students listed:

1. Prof. Poul Erik Lindelöf the Niels Bohr Institute, Oersted Laboratory, University of Copenhagen, Denmark

Finn Berg Rasmussen, lecturerJesper Nygaard, lecturerKurt Gloos, research lecturerPawel Utko, PhD studentAne Jensen, PhD studentBrian Soerensen, PhD studentSoeren Erfurt Andresen, PhD studentKasper Grove Rasmussen, PhD studentMartin Aagesen, PhD student

2. Prof. Antti-Pekka JauhoMikroelektronik Centret (MIC), Technical University of Denmark (DTU), Denmark

Mads Brandbyge, associate professorTomas Novotny, post-docAndrea Donarini, ph.d student

Thomas Frederiksen, ph.d studentDan Bohr, Master's studentChristian Flindt, Master's studentAnders Mathias Lunde, Master's student

3. Prof. Pertti HakonenLow Temperature Laboratory, Helsinki University of Technology, Finland

M. Ahlskog, postdoc T. Heikkilä, postdocT. Lehtinen, Master's student R. Lindell, PhD student M. Paalanen, Prof., director of the Low Temperature Laboratory L. Roschier, PhD studentM. Sillanpää, PhD studentR. Tarkiainen, PhD studentV. Vaskelainen, Master's student

4. Prof. Jukka PekolaLow Temperature Laboratory, Helsinki University of Technology, Finland

Alexander Savin, PhD, senior researcherAnne Anthore, PhD, post-docJani Kivioja, PhD studentAntti Niskanen, PhD studentJouni Flyktman, PhD studentTommi Nieminen, master's student

5. Dr. Ilari MaasiltaDepartment of Physics, University of Jyväskylä, Finland

Sampsa Hämäläinen, PhD studentJenni Karvonen, PhD studentKimmo Kinnunen, PhD studentPanu Koppinen, PhD student Lasse Taskinen, PhD studentThomas Kuhn, PhD student (together with Prof. Matti Manninen)

6. Prof. Detlef HeitmannInstitut fur Angewandte Physik, University of Hamburg, Germany

Can-Ming Hu, senior researcher + studentsChristian Schuller, senior researcher + studentsDirk Grundler, senior researcher + students

7. Prof. Vidar GudmundssonScience Institute, University of Iceland, Iceland

Sigridur Sif Gylfadottir M.Sc. studentJens H. Bardason M.Sc. studentAndrei Manolescu Dr. coworker

8. Prof. Algirdas MatulisSemiconductor Physics Institute, Vilnuis, Lithuania

Nerija Zurauskiene, senior researcher

9. Prof. Arne BrataasDept. of Physics, Norwegian University of Science and Technology, Trondheim,Norway Jan Petter Morten, PhD studentJoern Foros, PhD studentRoman Shchelushkin, PhD studentJan Manschot, Master’s studentVictor Havik, project studentTorgeir Hansen project student

10. Prof. Eivind Hiis HaugeDept. of Physics, Norwegian University of Science and Technology, Trondheim,Norway

11. Prof. Yuri GalperinDept. of Physics, University of Oslo, Norway

Dragos-Victor Anghel, postdoc

12. Prof. Mats JonsonDept. of Applied Physics, Chalmers University of Technology and GöteborgUniversity, Sweden

Robert Shekhter Professor Jari Kinaret Associate professor Leonid Gorelik Researcher Magnus Jonsson PhD student Caroline Huldt PhD student Jaeuk Kim PhD student Dmyrto Fedorets PhD student Sven Axelsson Masters student

13. Prof. Koung-An ChaoDept. of Theoretical Physics, University of Lund, Sweden

A.G. Mal'shukov, Visiting Professor Vladislav Schlyapin, Postdoc Anders Blom, (Ph.D.) Research Engineer Karin Nilsson, Ph.D. Student

d) I nformation on scientific results 2003

Results are listed by groups:

Lindelöf:

The research in 2003 has concentrated on 1) transport in carbonnanotubes, 2) magnetic semiconductors and spin injection, and 3) SAWdriven Quantum Point Contacts.We have in particular studied Ramanspectroscopy in carbon nanotubes allowing determination ofchiralities. Peapod nanotubes have been studied and we have succeededto grow carbon nanotubes epitaxially into III-V heterostructures, - a

result of considerable practical importance. Optimization of theinjection of polarized electrons into III-V semiconductor promise wellfor the continuing studies of nanomagnetism. Theproject SAWPHOTON aiming at high frequency generation of singlephotons on demand is progressing.

Publications 2003:

"Direct Capacitive Coupling of Josephson Oscillations to a QuantumPointContact", S.E. Andresen, A. Kristensen and P. E. Lindelof, in TowardtheControllable Quantum State (editors: H. Takayanagi and J. Nitta, WorldScienctific, New Jersey 2003), p. 295 (2003).

"Effect of annealing on carrier density and Curie temperature inepitaxial(Ga,Mn)As thin films", B. S. Sørensen, J. Sadowski, R. Mathieu, P.Svedlindh, and P. E. Lindelof, Appl. Phys. Lett. 82, 2287 (2003).

"Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAsinterface", S. E. Andresen, B. S. Sørensen, F. B. Rasmussen, P. E.Lindelof,J. Sadowski, C. M. Guertler, and J. A. C. Bland, J. Appl. Phys. 94,3990(2003)

"Magnetization of ultrathin (Ga,Mn)As layers", R. Mathieu, B. S.Sørensen,J. Sadowski, J. Kanski, P.Svedlindh, P.E. Lindelof, D. Hrabovsky, andE.Vanelle, Cond-mat/0208411 (2003)

"Ferromagnetic GaMnAs Thin Films", B. S. Sørensen, J. Sadowski, S. E.Andresen, P. E. Lindelof, R. Matheu, P. Svedlindh and J. Kanski.Proceedings of the 26th International Conference on the Physics ofsemiconductors (ICPS) 2002. (Edited by J. H. Davies and A. R. Long.Institute of Physics 2003).

"Magnetic anisotropy of tunneling in GaMnAs based structures", S. E.Andresen, J. Sadowski, B. S. Sørensen and P.E. Lindelof, Proceedingsof the26th International Conference on the Physics of semiconductors (ICPS)2002.(Edited by J. H. Davies and A. R. Long. Institute of Physics 2003).

"Screening behavior of the two-dimensional metallic state in

silicon-on-insulator structures", G. Pillwein, A. Prinz, G.Brunthaler, P.E.Lindelof, and J. Ahopelto, Proceedings of the 26th InternationalConferenceon the Physics of Semiconductors ICPS) 2002 (Edited by J. H. Daviesand A.R. Long. Institute of Physics 2003).

"Single-electron transportdriven by surface acoustic waves throughshallow-etched point contacts", P. Utko, K. Gloos, J.B. Hansen, andP.E.Lindelof, Acta Phys. Pol. In press (2003),

Jauho:

We have developed a quantum theory of the shuttle instability(invented by the Chalmers group in 1998) through a nanostructurewith a mechanical degree of freedom. A phase space formulation interms of the wigner function allows us to identify a crossover fromthe tunneling to the shuttling regime, thus extending thepreviously found classical results to the quantum domain. Furthera new dynamical regime is discovered, where the shuttling is drivneexclusively by the quantum noise. Finally, we have developed aformalism to calculate the noise in a quantum dot array with internalmechanical motion.

Publications 2003:

1. Nonequilibrium Green FunctionModelling of Transport in Mesoscopic Systems, A.~P.~Jauho, in{\sl Progress in Nonequilibrium Green's Functions II}, pp. 181 --188, ed. M.~Bonitz, World Scientific (2003).

2. Quantum Shuttle in Phase Space, T. Novotny, A. Donarini, and A. P. Jauho, Phys.Rev. Lett. {\bf 90}, 256801 -- 256804 (2003).

3. Virtual photon contribution to frictional drag in double-layerdevices},A. Donarini, R. Ferrari, A. P. Jauho, and L. Molinari, PhysicsLetters A {\bf 312}, 123 -- 129 (2003).

4. TMR Effect in a FM-QD-FM system, F. M. Souza, J. C.Egues, and A. P. Jauho, to appear in Brazilian Journal of Physics(2004).

5. Coulomb drag in multi-wall carbonnanotubes, A. M. Lunde and A. P. Jauho, to appear in Semiconductor Science and Technology (2004).

6. Shuttle Instabilities: Semiclassical Phase Analysis, A. Donarini,T. Novotn{\'y}, and A. P. Jauho, to appear in Physica E (2004).

7. Quantum theory of shuttle instability}, T.Novotn{\'y}, A. Donarini, and A. P. Jauho, to appear inSemiconductor Science and Technology (2004).

8. Conductance switching in a molecular device: the role

of sidegroups and intermolecular interaction, Jeremy Taylor, Mads Brandbyge, Kurt Stokbro,Phys. Rev. B 68, 121101 (2003)

9. Conductance of single-atom platinum contacts: Voltage-dependence of the conductance histogram,S.K. Nielsen, Y. Noat, M. Brandbyge, R.H.M. Smit, K. Hansen, L.Y.Chen, A.I. Yanson, F. Besenbacher, J.M. van RuitenbeekPhys. Rev. B 67, 245411 (2003).

10. Origin of current-induced forces in an atomic gold wire: A first-principles study, Mads Brandbyge, Kurt Stokbro, Jeremy Taylor,José-Luis Mozos, and Pablo OrdejónPhys. Rev. B 67, 193104 (2003).

Hakonen :

We have improved the sensitivity of the Bloch oscillating transistor(BOT) and shown that the equivalent input current noise may be lessthan the shot noise of its input base current. Simultaneously with thedevelopment of BOTs, we have studied the prospects of high-sensitivitynoise spectroscopy using a Coulomb-blockaded, mesoscopic Josephsonjunction as a detector. We have also developed a new type ofelectrometer which is based on the measurement of kinetic inductanceof a superconducting SET. This device yields similar characteristicsas the rf-SET but it works at power levels oftwo orders magnitude smaller.

Publications:

1) J. Delahaye, J. Hassel, R. Lindell, M. Sillanpää, M. Paalanen, H.Seppä,and P. Hakonen, Low Noise Current Amplifier based on MesoscopicJosephsonJunction, Science 299, 1045 – 1048 (2003).

2) R. Lindell, J. Penttilä, M. Paalanen, and P. Hakonen, SpectroscopyofMesoscopic Josephson Junction using Inelastic Cooper-pair Tunneling,PhysicaE 18, 13 – 14 (2003).

3) J. Delahaye, J. Hassel, R. Lindell, M. Sillanpää, M. Paalanen, H.Seppä,and P. Hakonen, Bloch Oscillating Transistor - a New MesoscopicAmplifier,Physica E 18 , 15 – 16 (2003).

4) J. Delahaye, R. Lindell, M. Sillanpää, M. Paalanen, E. Sonin, andP.Hakonen, Coulomb-blockaded Josephson Junction as a Noise Detector,Journalof the Physical Society of Japan 72, Suppl. A, 187 – 188 (2003).

5) R. Lindell, J. Penttilä, M. Sillanpää, and P. Hakonen, Measuringthe

Quantum States of a Mesoscopic SQUID using a Small Josephson Junction,Phys.Rev. B 68, 052506 – 052509 (2003).

6) J. Delahaye, T. Heikkilä, R. Lindell, M. Sillanpää, T. Yamaguchi,P.Hakonen, and E. Sonin, Ultrasensitive Noise Measurement Scheme forMesoscopic Circuits using a Coilomb Blockaded Josephson Junction,Proc. of17th Int. Conf. Noise and Fluctuations, pp. 455 – 460.

7) L. Roschier, P. Hakonen, K. Bladh, P. Delsing, K.W. Lehnerty, L.Spietz,and R.J. Schoelkopf, Noise performance of the RF-SET, J. Appl. Phys.inprint.

8) R. Tarkiainen, M. Ahlskog, A. Zyuzin, P. Hakonen, and M. Paalanen,Transport in strongly disordered multiwalled carbon nanotubes, Phys.Rev. B.in print.

9) J. Hassel, J. Delahaye, H. Seppä, and P. Hakonen, Control ofCoulombBlockade in a Mesoscopic Josephson Junction using Single ElectronTunnelling, Phys. Rev. B to be published.

10) L. Roschier, T. Heikkilä, and P. Hakonen, Cyclostationary shotnoise inmesoscopic measurements, submitted to Appl. Phys. Lett.

Pekola:

I have founded a new research group ("PICO") at Low TemperatureLaboratory at HUT in 2003, which works in close collaboration with theexisting mesoscopic research group ("NANO") at LTL. The mainactivities of my group are within accurate Cooper pair pumping and itsquantum corrections, thermal effects in mesoscopic structures, andmacroscopic quantum tunnelling in Josephson junctions and SQUIDs formeasurements of superconducting quantum bits.

Publications:

J. Kinnunen, P. Torma, and J. P. Pekola, Measuring charge-basedquantum bitsby a superconducting single-electron transistor, Phys. Rev. B 68,020506(R)(2003).

A. Luukanen, K. M. Kinnunen, A. K. Nuottajärvi, H. F. C. Hoevers, W.M.Bergmann Tiest, and J. P. Pekola, Fluctuation-limited noise in atransition-edge sensor, Phys. Rev. Lett. 90, 238306 (2003).

K. Gloos, P. J. Koppinen, and J. P. Pekola, Properties of nativeultrathinaluminum oxide tunnel barriers, J. Phys.: Condens. Matter 15, 1733(2003).

P. Kivinen, A. Savin, M. Zgirski, P. Törmä, J. Pekola, M. Prunnila,and J.Ahopelto, Electron-phonon heat transport and electronic thermalconductivityin heavily doped silicon-on-insulator film, J. Appl. Phys. 94, 3201(2003).

W. X. Huang, P. Dendooven, K. Gloos, N. Takahashi, J. P. Pekola, andJ.Äystö, Extraction of radioactive ions across the surface of superfluidhelium: A new method to produce cold radioactive nuclear beams,Europhys.Lett., 63, 687 (2003).

O. Buisson, F. Balestro, J. P. Pekola, and F. W. J. Hekking, One shotquantum measurement using a hysteretic DC-SQUID, Phys. Rev. Lett. 90,238304(2003).

A. Luukanen and J. P. Pekola, A superconducting antenna-coupled hot-spotmicrobolometer, Appl. Phys. Lett. 82, 3970 (2003).

R. Fazio, F. W. J. Hekking, and J. P. Pekola, Measurement of coherentchargetransfer in an adiabatic Cooper pair pump, Phys. Rev. B 68, 054510(2003).

M. Meschke, J. P. Pekola, F. Gay, R. E. Rapp, and H. Godfrin, Electronthermalization in metallic islands probed by Coulomb blockadethermometry,submitted to J. Low Temp. Phys. (2003).

F. Balestro, J. Claudon, J. P. Pekola, and O. Buisson, Evidence oftwo-dimensional macroscopic quantum tunneling of a current-biased DC-SQUID,Phys. Rev. Lett. 91, 158301 (2003).

Antti O. Niskanen, Jukka P. Pekola, and Heikki Seppä, Fast andaccuratesingle-island charge pump: Implementation of a Cooper pair pump, Phys.Rev.Lett. 91, 177003 (2003).

J. P. Pekola, T. T. Heikkilä, A. M. Savin, J. T. Flyktman, F.Giazotto, andF. W. J. Hekking, Limitations of electron cooling, submitted (2003).

J. J. Toppari, G. S. Paraoanu, A. M. Halvari, and J. P. Pekola,Elasticcotunnelling of quasiparticles in superconducting Al/Nb/Al singleelectrontransistor, submitted (2003).

J. J. Toppari, J. M. Kivioja, J. P. Pekola, and M. T. Savolainen,Turnstilebehaviour of the Cooper-pair pump, submitted (2003).

F. Giazotto, T. T. Heikkilä, F. Taddei, Rosario Fazio, J. P. Pekola,and F.

Beltram, Tailoring Josephson coupling through superconductivity-inducednonequilibrium, submitted (2003).

Maasilta:

We have studied thermal properties of mesoscopic metallic island withthe help of SINIS tunnel junction thermometry. We have observed forthe first time that in regular evaporated Cu, the energy loss ratebetween electrons and thermal phonons follows the expected power lawin the disordered limit. We also see the transition to the clean limitwhen temperature is raised. In addition we have developed an actechnique to measure this electron-phonon interaction more accurately.We have also continued to develop superconducting transition-edgesensors (TES) for X-ray calorimetry. New low-noise SQUID-basedamplifier setup has been developed for evaluation of the resolutionlimiting noise mechanisms in TESs.

Publications:

1.Electrons and phonons at sub-Kelvin temperatures: validation of thedisorder-mediated scattering theory I. J. Maasilta, J. T. Karvonen, J. M. Kivioja, and L. J. Taskinensubmitted to Phys. Rev. Lett., cond-mat/0311031

2.Modeling electric field sensitive scanning probe measurements for atip of arbitary shapeI. Kuljanishvili, S. Chakraborty, I. J. Maasilta, S. H. Tessmer, andM. R. Mellochsubmitted to Ultramicroscopy, cond-mat/0309667

3.Imaging a two-dimensional electron system with a scanning chargedprobeS. Chakraborty, I. J. Maasilta, S. H. Tessmer, and M. R. Mellochsubmitted to Phys. Rev. B.

4.Critical fluctuations as a source of excess noise in a TES in aCorbino geometryA. Luukanen, W. M. Bergmann Tiest, H. F. C. Hoevers, K. M. Kinnunen,I. J. Maasilta, A. K. Nuottajärvi, and J. P. Pekolato appear in Nucl. Instr. and Meth. A

5.Direct observation of micron-scale ordered structure in a two-dimensional electron systemI. J. Maasilta, S. Chakraborty, I. Kuljanishvili, S. H. Tessmer, andM. R. MellochPhys. Rev. B. 68, xxx (2003), cond-mat/0205191.

6.Tunneling images of a two-dimensional electron system in a quantizingmagnetic fieldI. J. Maasilta, S. Chakraborty, I. Kuljanishvili, S. H. Tessmer, andM. R. MellochPhysica E: Low-dimensional Systems and Nanostructures 18, 167 (2003).

7.Response time of a thermometer based on normal metal-insulator-superconductor (NIS) tunnel junctionsJ. M. Kivioja, I. J. Maasilta, J. T. Karvonen, and J. P. PekolaPhysica E: Low-dimensional Systems and Nanostructures 18, 21 (2003).

Gudmundsson:

In cooperation with Andrei Manolescu at deCode in Reykjavik and C.-S.Tang in HsinChu in Taiwan I have focused the research on time-dependent phenomena in two-dimensional electron gas in nanostructures.We have investigated how a short THz pulse of electromagneticradiation changes in the persistent current in quantum rings withfinite width. We have calculated the nonlinearresponse of a short quantum wire to an intensive THz pulse, and foundhow both collective spin- and density oscillations can be excited.Together with Sigridur Sif we have compared the results for thefinite width ring to a 1D ring. Jens H. Bardarson is working ontransport through molecules.

Publications:

The orbital magnetization of single and double quantum dots in a tightbinding model, A. Aldea, V. Moldoveanu, M. Nita, A. Manolescu, V. Gudmundsson, B.Tanatar, Phys. Rev. B67, 035324 (2003), (cond-mat/0207307). Non-adiabatic current generation in a finite width semiconductor ring, Vidar Gudmundsson, Chi-Shung Tang, Andrei Manolescu, Phys. Rev. B67, 161301(R) (2003), (cond-mat/0301020). Impurity and spin effects on the magneto-spectroscopy of a THz-modulated nanostructure, Vidar Gudmundsson, Chi-Shung Tang, Andrei Manolescu, Phys. Rev. B68, 165343 (2003), (cond-mat/0304571). Non-adiabatic Current Excitation in Quantum Rings, S. S. Gylfadottir, V. Gudmundsson, C. S. Tang, and A. Manolescu, Physica Scripta T, submitted (2003), 20th Nordic Semiconductor Meeting, Tampere (2003), (cond-mat/0309661).

Brataas:

G. E. W. Bauer, A. Brataas, Y. Tserkovnyak, B. I. Halperin, M.Zwierzycki, P. J. Kelly, Dynamic ferromagnetic proximity effectin photoexcited semiconductors, submitted to Phys. Rev. Lett.

E. G. Mischenko, A. Brataas, and Y. Tserkovnyak, Spin detectionin quantum dots by electric currents, submitted to Phys. Rev.Lett.

J. Johansson, V. Korenivski, D. B. Haviland, and A. Brataas,Giant fluctuations of superconducting order paramter inFerromagnet/superconductor single electron transistors,submitted to Phys. Rev. Lett.

J. Manschot, A. Brataas, and G. E. W. Bauer, Non-monotonicangular magnetoresistance in asymmetric spin valves, submittedto Phys. Rev. B Rapid Communications.

Galperin:

1. A. Brataas, G. Zarand, Y. Tserkovnya, and G. E. W.Bauer, Magnetoelectronic Spin Echo, to be published inPhys. Rev. Lett. (2003).

2. B. Heinrich, Y. Tserkovnyak, G. Woltersdorf, A.Brataas, R. Urban, and G. E. W. Bauer, Dynamic ExchangeCoupling in Magnetic Bilayers, Phys. Rev. Lett. 90,187601 (2003).

3. G. E. W. Bauer, A. Brataas, and Y. Tserkovnyak,Spin-torque Transistor, Appl. Phys. Lett. 82, 3928(2003)

4. A. A. Kovalev, G. E. W. Bauer, and A. Brataas,Magnetovibrational Coupling in small Cantilevers, Appl.Phys. Lett. 83, 1584 (2003).

5. G. E. W. Bauer, Y. Tserkovnyak, D. Huertas-Hernando,A. Brataas, From Digital to AnalogueMagnetoelectronics: Theory of Transport in Non-Collinear Magnetic Nanostructures, to be published inAdvance in Solid State Physics, edited by B. Kramer,Springer-Verlag, Berlin, 2003

6. Y. Tservkonyak, A. Brataas, and G. E. W. Bauer,Dynamic Exchange Coupling and Gilbert Damping inMagnetic Multilayers, J. Appl. Phys. 93, 7534 (2003).

7. G. Zarand, A. Brataas and D. Goldhaber-Gordon,Kondo Effect and Spin Filtering in TriangularArtificial Atoms, Solid State Commun. 126, 463 (2003).

8. Y. Tservkonyak, A. Brataas and G. E. W. Bauer,Dynamic Stiffness of Spin Valves, Phys. Rev. B Rap. Com.67, 094421 (2003).

9. G. E. W. Bauer, Y. Tserkovnyak, D. Huertas-Hernando, A. Brataas, Universal AngularMagnetoresistance and Spin Torque inFerromagnetic/Normal Metal Hybrids, Phys. Rev. B 67,094421 (2003).

Below main projects carried out by the group are reported in the form of main publishedarticles and brief abstracts. The period covered is from the last half of 2002 till thepresent time.

Nano-electromechanics1. Shekhter, RI, Galperin, YM, Gorelik, LY. Isacsson, A, Jonson, M

“Shuttling of electrons and Cooper pairs” (review)JOURNAL OF PHYSICS-CONDENSED MATTER, 15, R441 (2003)

Properties of nanocomposite materials are affected by a coupling between mechanicaldeformations of the materials and electronic charge transport. In one of the simplest systems ofthis kind, a single electron transistor (SET) with deformable tunnel barriers(nanoelectromechanical SET), mechanically assisted charge transfer becomes possible. This canbe viewed as 'shuttling of single electrons' between metallic leads by a movable small-sizedcluster. In this article we review some recent theoretical and experimental achievementsconcerning shuttle transport, in normal as well as superconducting systems.

2. Isacsson, A, Gorelik, LY, Shekhter, RI, Galperin, YM, Jonson, M“Mechanical cooper pair transportation as a source of long-distancesuperconducting phase coherence”

PHYSICAL REVIEW LETTERS, 89, 277002 (2003).

Transportation of Cooper pairs by a movable single Cooper-pair box placed between two remotesuperconductors is shown to establish coherent coupling between them. This coupling is due toentanglement of the movable box with the leads and is manifested in the suppression of quantumfluctuations of the relative phase of the order parameters of the leads. It can be probed byattaching a high resistance Josephson junction between the leads and measuring the currentthrough this junction. The current is suppressed with increasing temperature.

3. Shekhter, RI, Gorelik, LY, Isacsson, A, Galperin, YM, Jonson, M“Nanoelectromechanics of Coulomb Blockade nanostructures” (review)PHYSICA SCRIPTA, T102, 13 (2002)

The aim of this paper is to emphasize the role of coupling between electronic and mechanicaldegrees of freedom taking place on a nanometer length scale. Such coupling affects significantlythe electrical properties of nanocomposite materials which are usually heteroconducting andheteroelastic by their nature. As examples of nanoelectromechanics in normal andsuperconducting composites a self-assembled single electronic device exhibiting a dynamicalinstability leading to shuttling of electrical charge by a movable Coulomb dot is discussed alongwith an example of shuttling of Cooper pairs by a movable Single Cooper Pair Box.

Low-dimensional metallic and semiconductor systems4. Drichko, IL, Diakonov, AM, Smirnov, IY, Preobrazhenskii, VV, Toropov, AI,Galperin, YM

“DX-centers and long-term effects in the high-frequency hopping conductancein Si-doped GaAs/Al0.3Ga0.7As heterostructures in the quantum Hall regime:acoustical studies”

PHYSICA E-LOW-DIMENSIONAL SYSTEMS &NANOSTRUCTURES, 17, 276 (2003).

It is discovered that both high-frequency (hf) hopping conductance and electron density in the2D channel, n(s), in Si delta-doped and modulation-doped GaAs/Al0.3Ga0.7As heterostructuresat the plateaus of the integer quantum Hall effect depend on cooling rate of the samples.Furthermore, consecutive IR illumination leads to a persistent hf hopping photoconductance,which decreases when the illumination intensity increases, while n(s) increases. The persistenthf hopping photoconductance occurs when the illumination frequency exceeds a threshold,which is between 0.48 and 0.86 eV. The results are attributed to two-electron defects (so-calledDX-centers) located in the Si-doped layer of the Al 0.3 Ga 0.7As heterostructure.

5. Goppert, G, Galperin, YM, Altshuler, BL, Grabert, H

“Magnetic-field effects in energy relaxation mediated by Kondo impurities inmesoscopic wires”

PHYSICAL REVIEW B, 66, 195328 (2002)

We study the energy distribution function of quasiparticles in short voltage biased mesoscopicwires in the presence of magnetic impurities and applied magnetic field. The system is describedby a Boltzmann equation where the collision integral is determined by coupling to spin-1/2impurities. We develop a theory of the coupling of nonequilibrium electrons to dissipative spins.This theory is valid as long as the characteristic smearing of the steps in the energy distributionfunction, which depends both on the bias voltage and the location of the probe, exceeds theKondo temperature. We further address the renormalization of coupling constants bynonequilibrium electrons. Magnetic-field dependence of the energy relaxation rate turns out tobe nonmonotonic. For low magnetic field an enhancement of energy relaxation is found,whereas for larger magnetic fields the energy relaxation decreases again meeting qualitativelythe experimental findings by Anthore (cond-mat/0109297). This gives a strong indication thatmagnetic impurities are in fact responsible for the enhanced energy relaxation in copper wires.Our theoretical results are in good agreement with the experiment at large bias voltages wherethe theory is applicable. At the same time, at small bias voltages there are substantialquantitative deviations. Furthermore, the concentration of the spins, which follows from theenergy relaxation for Cu, seems to to be substantially higher than the concentration estimatedfrom weak localization (dephasing rate) measurements. Since the approach presented is validonly above Kondo temperature, it does not apply to the related problem of weak localization atlow temperature in equilibrium.

Nanoscopic detectors6. D. V. Anghel and L. Kuzmin,

“Capacitively coupled hot-electron nanobolometer as far-infrared photoncounter,”

Appl.Phys. Lett. 82 , 293-295 (2003) , Virtual Journal of NanoscaleScience Technology , vol. 7 , Issue 3 (2003) , cond-mat/0212288.

We show theoretically that hot-electron nanobolometers consisting of a small piece of normalmetal, capacitively coupled to a superconducting antenna through a pair of normal metal–insulator–superconductor (NIS) tunnel junctions may be used as far-infrared photon counters. Tomake the device most effective at high counting rates, we suggest the use of the bolometer in thesimplest configuration, when the NIS tunnel junctions are used as both an electron cooler andthermometer. The absorbtion of the photon in the normal metal produces a pulse in the electrontemperature, which is measured by the NIS junctions. The counter may resolve photons up to0.3–0.4 mm wavelength and has a typical re-equilibration time constant of about 20 ns.

Statistical mechanics of mesoscopic systems7. D. V. Anghel,

“Gases in two dimensions: universal thermodynamics and its consequences,”

J. Phys. A: Math. Gen. 35 , 7255-7267 (2002) , cond-mat/0105089.

I discuss ideal and interacting quantum gases obeying general fractional exclusion statistics. Forsystems with constant density of single-particle states, described in the mean fieldapproximation, the entropy depends neither on the microscopic exclusion statistics, nor on theinteraction. Such systems are called thermodynamically equivalent and I show that themicroscopic reason for this equivalence is a one-to-one correspondence between the excitedstates of these systems. This provides a method, different from the bosonization technique, oftransforming between systems of different exclusion statistics. In the last section themacroscopic aspects of this method are discussed.

In appendix A, I calculate the fluctuation of the ground-state population of a condensed Bosegas in a grand-canonical ensemble and mean field approximation, while in appendix B I show asituation where although the system exhibits fractional exclusion properties on microscopicenergy intervals, a rigorous calculation of the population of single-particle states reveals acondensation phenomenon. This also implies a malfunction of the usual and simplifiedcalculation technique of the most probable statistical distributions.

8. D. V. Anghel, “Condensation in ideal Fermi gases,”

J. Phys. A: Math. Gen. 36 , L577-L583 (2003) ; cond-mat/0310248.

I investigate the possibility of condensation in ideal Fermi systems of general single-particledensity of states. For this I calculate the probability wN0 of having exactly N0 particles in thecondensate and analyze its maxima. The existence of such maxima at macroscopic values of N0

indicates a condensate. An interesting situation occurs for example in 1D systems, where wN0

may have two maxima. One is at N0 = 0 and another one may exist at finite N0 (fortemperatures below a certain condensation temperature). This suggests the existence of a first-order phase transition. The calculation of wN0 allows for the exploration of ensembleequivalence of Fermi systems from a new perspective.

Vortex Avalanches in Superconductors9. D. V. Shantsev, P.E.Goa, F.L.Barkov, T.H.Johansen, W. N. Kang, S. I. Lee

“Interplay of dendritic avalanches and gradual flux penetration insuperconducting MgB2 film”

Supercond. Sci. Technol. 16, 566-570 (2003).

Magneto-optical imaging was used to study a zero-field-cooled MgB2 film at 9.6 K where in aslowly increasing field the Abrikosov vortices penetrate via an abrupt formation of dendriticstructures consisting of narrow branching channels. Simultaneously, a gradual flux penetrationtakes place, eventually covering the dendrites, and a detailed analysis of this process is reported.We find an anomalously high gradient of the flux density across a dendrite branch, and a peakvalue that decreases as the applied field increases. This unexpected behaviour is reproduced byflux creep simulations based on the non-local field–current relation in the perpendiculargeometry. The simulations also provide indirect evidence that flux dendrites are formed at anelevated local temperature, consistent with a thermo-magnetic mechanism of the instability.

10. F. L. Barkov, D. V. Shantsev, T. H. Johansen, P. E. Goa, W. N. Kang, H. J. Kim, E.M. Choi, S. I. Lee

“Local threshold field for dendritic instability in superconducting MgB2 films”

Phys. Rev. B 67, 064513 (2003)..

Using magneto-optical imaging the phenomenon of dendritic flux penetration insuperconducting films was studied. Flux dendrites were abruptly formed in a 300-nm-thick filmof MgB2 by applying a perpendicular magnetic field. Detailed measurements of flux densitydistributions show that there exists a local threshold field controlling the nucleation andtermination of the dendritic growth. At 4 K the local threshold field is close to 12 mT in thissample, where the critical current density is 10^7 A/cm^2 . The dendritic instability in thin filmsis believed to be of thermomagnetic origin, but the existence of a local threshold field and itssmall value are features that distinctly contrast with the thermomagnetic instability (flux jumps)in bulk superconductors.

Magneto-Elastic effects in Superconductors11. Tom H. Johansen and Daniel V. Shantsev

“Magnetostrictive behaviour of thin superconducting disks”

Supercond. Sci. Technol., 16, 1109-1114 (2003).

Vortex-pinning-induced stress and strain distributions in a thin disksuperconductor in a perpendicular magnetic field are analysed. We calculate thebody forces, solve the magneto-elastic problem and derive formulae for allstress and strain components, including the magnetostriction. The flux andcurrent density profiles in the disk are assumed to follow the Bean model.During a cycle of the applied field the maximum tensile stress is found to occurapproximately midway between the maximum field and the remanent state. Aneffective relationship between this overall maximum stress and the peak field isfound.

1. Irina L. Drichko, Andrey M. Diakonov, Veniamin I. Kozub, Ivan Yu. Smirnov, YuriM. Galperin, Andrew I. Yakimov, Alexander I. Nikiforov

“AC-Hopping Conductance of Self-Organized Ge/Si Quantum Dot Arrays”cond-mat/0311267

Dense ($n=4 \times 10^{11}$ cm$^{-2}$) arrays of Ge quantum dots in Si host were studiedusing attenuation of surface acoustic waves (SAWs) propagating along the surface of apiezoelectric crystal located near the sample. The SAW magneto-attenuation coefficient,$\Delta\Gamma=\Gamma(\omega, H)-\Gamma(\omega, 0)$, and change of velocity of SAW,$\Delta V /V=(V(H)-V(0)) / V(0)$, were measured in the temperature interval $T$ = 1.5-4.2 Kas a function of magnetic field $H$ up to 6 T for the waves in the frequency range $f$ = 30-300MHz. Basing on the dependences of $\Delta\Gamma$ on $H$, $T$ and $\omega$, as well as onits sign, we believe that the AC conduction mechanism is a combination of diffusion at themobility edge with hopping between localized states at the Fermi level. The measured magneticfield dependence of the SAW attenuation is discussed basing on existing theoretical concepts.

2. A.V.Bobyl, D.V.Shantsev, Y.M.Galperin, A.A.F.Olsen, T.H.Johansen, W.N.Kang,S.I.Lee

“Mesoscopic flux jumps in MgB2 films visualized by magneto-optical imaging”cond-mat/0304603

We report on the first spatially resolved observation of mesoscopic flux jumps insuperconducting films. Magneto-optical imaging was used to visualize the flux penetration inMgB2 films subjected to a slowly varying perpendicular field. Below 10 K, flux jumps withtypical size 10-20 microns and regular shape are found to occur at random locations along theflux front. The total number of vortices participating in one jump is varying between 50 and10000. Simultaneously, big dendritic jumps with dimensions comparable to the sample size(10^6-10^8 vortices) are also found in this temperature range. We believe that both types ofjumps result from thermo-magnetic instability.

3. A. A. F. Olsen, H. Hauglin, T.H.Johansen, P. E. Goa and D.V.Shantsev“Single vortices observed as they enter NbSe2”Physics C, in press; cond-mat/0307248

We observe single vortices as they penetrate the edge of a superconductor using a high-sensitivity magneto-optical microscope. The vortices leap across a gap near the edge, a distancethat decreases with increasing applied field and sample thickness. This behaviour can beexplained by the combined effect of the geometrical barrier and bulk pinning.

4. D. V. Anghel,“Exclusion Statistics Transformation and Ensemble Equivalence Tested From aDifferent Perspective,”cond-mat/0310377The basic idea and main results of the ``exclusion statistics transformation'' (EST) areintroduced. Using EST, an ideal Fermi gas of general density of states is transformed into a Bosegas by preserving only the excitations in the system. The Bose gas is not ideal, and at lowtemperatures exhibits Bose-Einstein condensation, which is related to the Fermi condensation[D. V. Anghel, J. Phys. A: Math. Gen 36, L577-L583 (2003), cond-mat/0310248]. Byemphasizing the excitations in the system and the collective behavior of the condensate, the

bosonic description of the Fermi system may be better suited to describe Fermi systems at lowtemperatures. In the low temperature limit, the EST resembles the bosonisation technique. Theexistence of the condensate challenges the Fermi canonical-grandcanonical ensembleequivalence from a new point of view.

Jonson:

Within the network we mainly work on mesoscopic transport problems in systems where nanomechanical and electrical degrees of freedom arecoupled. Our 1998 PRL on "Shuttle mechanism for charge transfer inCoulomb blockade nanostructures" and the Nature article on "Coherenttransfer of Cooper pairs by a movable grain" from 2001 has started anew field with by now some 100 published papers from a number ofgroups. In [1] we reviewed this activity and presented some of ourmost recent results, see also [11]. In [6,7] we studied shuttletransport through a single molecule and developed the quantum dynamicsof both the mechanical and electronic degrees of freedom.

Nanoelectromechanics involving magnetic material is a more recentactivity where a first PRL publication [2] presented a new type ofexchange coupling between nanomagnets, controlled by electrostaticgate potentials. In [8] we proposed a new mechanism for a solid-stateTHz laser based on magnetic materials.

Another line of investigation has been nanoelectromechanical effectsin carbon nanotubes, where a nanorelay structure has been proposed and

studied [5]. The nanorelay is a three-terminal device that acts as aswitch in the GHz regime. Potential applications include logicdevices, memory elements, pulse generators, and current or voltageamplifiers

Publications:

1. R.I. Shekhter, Y.M. Galperin, L.Y. Gorelik, A. Isacsson, and M. Jonson: "Shuttling of electrons and Cooper pairs", J. Phys. C15, 441-469 (2003).

2. L.Y. Gorelik, R.I. Shekhter, V. Vinokur, D. Feldman, V.Kozub, and M. Jonson: "Electrical manipulation of nanomagnets", Phys. Rev. Lett. 91, 088301 (2003).

3. K. Engstrom, J.M. Kinaret, R.I. Shekhter, et al.: "Influence of electron-electron interactions on supercurrentin SNS structures", Low Temp Phys 29 (7): 546-550 (2003)

4. J.U. Kim, I.V. Krive, J.M. Kinaret: "Nonequilibrium plasmonsin a quantum wire single-electron transistor", Phys. Rev. Lett. 90, 176401 (2003)

5. J.M. Kinaret, T. Nord, S. Viefers: "A carbon-nanotube-based nanorelay", Appl Phys Lett 82 (8): 1287-1289 (2003)

6. D. Fedorets, "Quantum description of shuttle instability ina nanoelectromechanical single-electron transistor", Phys. Rev. B68, 033106 (2003)

7. D. Fedorets, L. Y. Gorelik, R. I. Shekhter, and M. Jonson: "Quantum theory of shuttle phenomena in ananoelectromechanical single-electron transistor", [cond-mat/0311105] (submitted to Phys. Rev. Lett.)

8. A. Kadigrobov, Z. Ivanov, T. Claeson, R. I. Shekhter, and MJonson: "Giant lasing effect in magnetic nanoconductors", [cond-mat/0306522] (submitted to Phys. Rev. Lett.)

9. I.V. Krive, L.Y. Gorelik, R.I. Shekhter, and M. Jonson: "Interplay of Rashba spin-orbit and Zeeman interactions inthe Josephson current through a ballistic Superconductor/Quantum

Wire/Superconductor junction, (submitted to Phys. Rev. B)

10. L.Y. Gorelik, S.I. Kulinich, R.I. Shekhter, and M. Jonson: "Resonant microwave properties of a voltage-biased single-Cooper-pair transistor", [cond-mat/0307568] (submitted to Phys. Rev. B)

11. T. Nord and A. Isacsson: "Impact of van der Waals forces onthe classical shuttle instability", cond-mat/0304511 (submitted to Phys. Rev. B)

Chao:

Our research topic within the NorFA Network is in the area spintronics. We study the three major topics : life time of spinpolarization, effieiency of spin injection and collection, andcoherence length of polarized spin current transport. The systems we investigate is III-V semconductorheterostructures in which the spin-orbit interaction (SOI)produces a large spin-split in electron energy levels. The spinpolarized current can be transported in a 2D channel made from III-V semiconductor heterostructures, and can be controlledby a side gate. It is so far the proved system for spintransport. Recently, our theory suggested two new directions: 1)a combined system of III-V semiconductor quantum well and a pn-junction serves as a good room temperature spin injector, and 2)an AC gate applied to a 2D electron gas can generate circular polarized spin current. We thus created a newarea of all-semiconductor functional system for spintronics. Ourpresent research topics involve spin dephasing effects,geometric spin phase, spin entanglement, optical excitation of

spin polarization, parametric spin pumping, and the role of optical phonons in spin relaxation. We have closecollaboration with experimental groups.

Publications:

1) V. A. Froltsov, A. G. Mal'shukov, K. A. Chao, "Spin-orbitinteraction and spin-charge interference in resonant Raman scattering fromIII-V semiconductor quantum wells", Phys. Rev. B {\bf 64} 73309(2001).

2) A. G. Mal'shukov and K. A. Chao, "Optoelectric spin injectionin semiconductor heterostructures without a ferromagnet", Phys.Rev. B - Rapid Commun. {\bf 65} 241308(R) (2002).

3) A. G. Mal'shukov, V. V. Shlyapin and K. A. Chao, "Quantumoscillations of spin current through a III-V semiconductor loop", Phys. Rev.B - Rapid Commun. {\bf 66} 081311(R) (2002).

4) W. M. Chen, I. A. Buyanova, G. Yu. Rudko, A. G. Mal'shukov,K. A. Chao, A. A. Toropov, Y. Ternet'ev, S. V. Sorokin, A. V. Lebedev, S. V.Ivanov, and P. S. Kop'ev, "Exciton spin relaxation in diluted magnetic semiconductor Zn$_{1-x}$Mn$_x$Se/CdSe superlattices: Effect ofspin splitting and the role of longitudinal optical phonons", Phys.Rev. B {\bf 67} 125313 (2003).

5) A. G. Mal'shukov and K. A. Chao, "Comment on 'Aharonov-Bohm Oscillations with Spin: Evidence for Berry's Phase'", Phys. Rev.Lett. {\bf 90} 179701-1 (2003).